Conventionally, there have been various kinds of ball mill-type mills as a device for obtaining recycled aggregate from scrap materials of concrete or asphalt. Many of them have dram bodies whose internal portions are divided by several milling plates (divider plates) in order to extend residence time of a to-be-milled material(s). In such mills, the to-be-milled material are moved from one end to the other end of the drum both through a gap between peripheral edge parts of the milling plates and walls inside the drum body as they are milled by a ball (a milling media) in each divided section.
This kind of conventional mill was attached such that its milling plate intersected at a right angle to a central shaft, and therefore it made impossible to positively move the ball in a front-back direction (in a shaft length direction of the drum body). As a result, the ball mostly used to move toward a radial direction and a circumferential direction. It therefore caused a ball and a to-be-milled material to rotate at uniform velocity, i.e. so called “an accompanying rotation” phenomenon, leading to significant decrease in mill efficiency.
In order to solve these problems, the applicant has already proposed a mill that can remarkably improve the mill efficiency by preventing the above-described accompanying rotation phenomenon from generating (see the following patent documents 1 and 2). The inventions described in the patent documents 1 and 2 can positively move a milling media (a ball etc.) in a front and back direction by attaching a milling plate so that it is inclined with respect to the plane intersecting the central shall, at a right angle. So to speak, they added to the milling plate the function of an agitating blade.
However, the conventional ball-mill type mills including, the mills in the patent documents 1 and 2 had a problem of making a loud noise. After examining, the applicant discovered that the main reason for the loud noise was due to big noise generated by clash between the ball and the to-be-milled material, and the ball and a drum body, especially, the latter.